Recently, an input detection device, which has a touch detection function capable of detecting the proximity (hereinafter including contact) of an external object and is referred to as a so-called touch panel, has attracted attention as an input detection device. The touch panel is provided as a display device, for example, as a display device with the touch detection function, which is mounted on a liquid crystal display device or is integrated into the liquid crystal device.
There is a touch panel capable of using, for example, a pen as an external object. By using the pen, for example, a small area is designated, and a handwritten character can be inputted. There are various techniques of detecting the touch made by the pen. One of the various techniques is an electromagnetic induction method. The electromagnetic induction method is capable of achieving high precision, for example, high writing-pressure detection precision and is also capable of achieving a hovering detection function in which the external object is apart from a touch panel surface. Thus, the electromagnetic induction method is important as a technique of detecting the touch of the pen.
There is a touch detection device capable of detecting a finger(s) etc. as an external object. In this case, since an object to be detected is different from the pen, a method different from the electromagnetic induction method is adopted as a technique of detecting the touch. For example, there are methods of detecting an optical variation, a resistance-value variation, and an electric field variation that occur due to the finger. An example of the method of detecting the electric-field variation among the methods is a capacitance method using capacitance. The capacitance method includes a relatively simple structure and achieves low power consumption, and thus is used for a portable information terminal etc.
A technique relating to the electromagnetic-induction-method touch panel is described in Patent Document 1 (Japanese Patent Application Laid-open No. H10-49301, for example.